Page 98
Criterion Duration (T
C
)
The Criterion Duration is the time required for a constant sound level that is
equal to the Criterion Level to produce a Noise Dose of 100%. Typically the
Criterion Duration is 8 hours.
For example, if: -
Criterion Sound Level = 85dB
Criterion Duration = 8 Hours
Then a sound level of 85dB for an 8 hour period will produce a Noise Dose of
100%.
Criterion Sound Level (L
C
)
The Criterion Sound Level is the sound level that if continually applied for the
Criterion Duration will produce a Noise Dose of 100%.
Castle instruments are defaulted to the upper exposure action value of 85dB for
the Criterion Sound Level but this is generally user selectable to allow for
legislation changes with selections available of 75, 80, 85 or 90dB.
See also ‘Exchange Rate’.
Daily Personal Noise Exposure Level (Lep,d)
Lep,d represents the total noise received by an employee at work and is
normalized to an 8 hour day. It is an essential requirement for the Noise at
Work Regulations 2005.
The overall Lep,d can be determined using partial exposures for different
locations and different exposure times of the employee or the employee can
wear a dose meter for the whole working day.
Normally the Lep,d is calculated from using the equivalent continuous ‘A’
weighted sound pressure level LAeq.
See ‘Function Equations’ to see how Lep,d is described mathematically.
In practice when measuring noise it is possible to take Lep,d readings with your
instrument of short duration i.e. less than five minutes (providing all variations of
noise emissions are covered). If the measured environment changes greatly,
then the longer the Lep,d reading is taken, the more accurate the measurement
will be.
